The present invention relates to a system of transportation wherein two or more modes of transportation are used to transport freight containers. The potential efficiencies and advantages associated with such a system have been well documented. For example, see U.S. Pat. Nos. 4,385,857 and 4,597,337 to Willetts and U.S. Pat. No. 4,669,391 to Wicks et al.
Generally, the most efficient intermodal transport systems are those which combine rail transport with truck and/or ship transport. The present invention is particularly directed to a rail/road intermodal transport system; however, the freight containers employed in the system of the present invention are also adapted for transport by ship.
This invention pertains to a bogie intended to be placed between the ends of two freight containers, making it possible to transport the freight containers on rails. It is contemplated that the bogie also carries a self-contained train brake unit. The term "freight container" hereinafter indicates any container capable of carrying freight including, but not limited to, road trailers and ISO cargo containers.
The invention also pertains to a rail transportation system including a series of freight containers and a series of bogies of the aforementioned type placed between these freight containers.
The term "road trailer" hereinafter indicates a trailer type freight container that is normally transported by road using a tractor. This trailer has in its rear part one or more running carriages composed of wheels equipped with tires and in its front part means allowing it to be attached in a removable manner to the upper part of the rear chassis of the tractor.
The invention also pertains to locking devices for securing freight containers to bogies.
The invention further pertains to a trailer construction particularly adapted for use in an intermodal transport system.
Freight containers have long been adapted to road/highway transport. The common truck trailer is an example of a freight container adapted for highway transport. However, the adaptation of freight containers of highway trailers to rail transport has presented problems.
Historically, several distinct approaches have been taken to the problem of transporting, by rail, freight containers which are adapted for highway use (e.g., truck road trailers).
The first such approach is the so called "piggy-back" approach wherein the road trailer is simply secured to a conventional or specially modified flat bed rail car. While this approach is relatively simple, it is inefficient in terms of weight and height.
In accordance with another approach, the rear part of the road trailer is equipped, in addition to the road running carriages, with a railroad axle having wheels adapted to travelling on rails. This railroad axle is normally kept in a position in which its wheels are located above wheels equipped with tires. These railroad wheels can be lowered to a level under the wheels equipped with tires to make travel on rails possible.
The front part of the trailer includes a rigidly attached drawbar so that it can be coupled to the rear of another identical trailer.
One drawback of this device lies in the fact that the presence of the railroad wheels makes the trailer considerably heavier.
Another approach is to support the ends of the freight containers on rail-trucks or bogies such that the freight container and bogie together act as a railroad car. This approach offers advantages in terms of height and weight by obviating the need for a flat deck supporting structure on which the containers are set. On the other hand, because the engine pull force and braking forces are transmitted through the freight containers, the freight containers are subject to forces resulting from the engine pull, the braking of the bogies and train forces.
Conventional truck trailers are not strong enough to withstand these forces. Accordingly, either the freight container or flat car deck used in connection with this approach must be specially designed and reinforced to withstand the torsional, tension and compression forces as well as the twisting moments resulting from engine pull, braking and uneven rails. A number of problems associated with prior bogie-type intermodal systems, such as those cited above, can be traced to a failure to adequately deal with these forces.
For example, in one construction the rear part of the road trailer is supported on a railroad bogie, through the use of a pivot. See e.g., U.S. Pat. No. 4,597,337. According to this solution, the trailers are coupled together using a rigidly attached drawbar which is also used to support the vertical load of the trailer located at the back of the bogie.
One disadvantage of this solution lies in the fact that the engine draft and buff forces are applied at the transverse center of the freight container which is typically the weakest point thereof rather than at the sides of the freight container which are strongest. Thus, application of force at the transverse center of the freight container necessitates additional reinforcement and/or provision of a force transfer means, thereby increasing the weight of the freight container.
Additionally, prior bogie designs have allowed play between the freight container and the bogie in an attempt to accommodate twisting freedom between them. This play, however, results in relatively quick wear of the components, and, accordingly, in the past, only a limited amount of play, and consequent accommodation, has been feasible.
Further, the operations for placing the trailers on rails, coupling the trailers and separating them are complex and costly. These operations indeed require heavy and complex handling equipment.
In the past, the respective freight containers have often been rigidly mounted to one another in order to avoid undesirable resonances. Although a rigid coupling is advantageous in some respects and widely employed throughout the railroad industry, it presents a significant disadvantage in the starting of the train convoy (string of rail cars) by the locomotive. More specifically, if each rail car of the convoy is rigidly coupled to one another, the locomotive must supply sufficient force to simultaneously initiate movement of each car in the convoy or string of trailers. Since a greater force is needed to initiate movement of the cars than to keep them moving, a maximum amount of drive force is required to begin movement of the train. While this problem could be overcome through the sequential starting of the cars by providing the slack connections between the cars, sequential starting is not practical in conventional arrangements, for example, because such slack would result in undesirable resonances between the cars.
Other solutions have been described, especially in French Patent 2,556,288 and U.S. Pat. Nos. 3,576,167, 4,669,391 and 4,687,399. None of the known solutions is truly satisfactory.
As noted above, many of the problems associated with previous attempts to employ rail trucks or bogies to support freight containers for rail transport may be broadly attributed to inadequate treatment of the forces acting on the containers resulting from a failure to recognize and appreciate the source and/or severity of these forces or to conceive of a solution for handling them in a practical manner.